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© Paweł Możejko Negative ion desorption from condensed molecules induced by low energy electrons Paweł Możejko Atomic Physic Group Department of Atomic Physics and Luminescence Faculty of Applied Physics and Mathematics Gdańsk University of Technology, Poland Department of Nuclear Medicine and Radiobiology Faculty of Medicine University of Sherbrooke, Canada © Paweł Możejko Interaction of charged particles with matter in the nature ... Photo by Bożena Żywicka-Możejko © Paweł Możejko ...and laboratory UHV conditions 10-10-10-11 Torr Vapor deposited films on metal substrate held at cryogenic temperatures (17 K< T <300K) Monochromatic electron beam produced by electrostatic monochromator (E~ 20-80 meV) ESD – electron stimulated desorption of anions as a function of incident electrons energy (yield function) and current © Paweł Możejko Applications Radiation damage to biomolecules from secondary electrons Dielectric aging Electron lithography Nanolithography Astrophysics © Paweł Możejko Experimental setup 10-10 Torr Monoenergetic electron beam E= 0-20 eV ∆E= 20-80 meV (FWHM) I0= 1 nA Uncertainty in the film thickness ~ 50 % Magnetic field reduced to less than 15 mG Target temperature T~20 K (17 K < T <300 K) © Paweł Możejko Intrinsic and extrinsic factors in ESD process Dissociative electron attachment (DEA) Dipolar dissociation (DD) e- + AB → AB*- → A- + B e-(E) + AB → (AB)* + e-(E’) → A- + B+ + e-(E’) Intrinsic effects modify and perturb TNI states during DEA and the electronically excited neutral states leading to DD Extrinsic effects influence the anion ESD process at times before the formation of the intermediate anion and after its decay Intrisic – interaction between TNI and the image charge it induces in the supporting molecular film and metal substrate – number of decay channels available for an autodetachment Extrinsic – electron scattering (and energy losses) prior to the formation of either the DEA or DD intermediate species – fragment anions interaction with their environment © Paweł Możejko Intrinsic, extrinsic and porosity effects in ESD of O- from O2 condensed on different substrates M.A. Huels, L. Parenteau, and L. Sanche, J. Chem. Phys. 100, 3940 (1994) Reduction in the DEA and DD processes !!! For condensed molecules DEA and DD are strongly perturbed by the surrounding medium i.e., the neighboring molecules and molecular solid surface © Paweł Możejko Interpretation problem How to differentiate between intrinsic and extrinsic factors influencing ESD anion yields © Paweł Możejko ESD of D- from deuterocarbons condensed on Kr and H2O films Saturated deuterocarbons: CD4, C2D6, C3D8 Unsaturated deuterocarbons: C2D2, C2D4 Substrates: clean platinum foil and multilayers of Kr and H2O ice of varying preparation Use of deuterated compounds permits us to discriminate between anion yields from ice and the molecular absorbate Rare gas solids provide an almost perfectly inert host surface – number and efficiency of extrinsic and intrinsic processes are very small – reference signal ! © Paweł Możejko ESD from pure films of condensed hydrocarbons Similar intensity for saturated and unsaturated hydrocarbons Mainly H- observed to desorb CH-, CH2-, CH3-,C2H- less than 1% of the intensity of the H- signal P. Rowntree, L. Parenteau, and L. Sanche, J. Phys. Chem. 95, 4902 (1991) © Paweł Możejko ESD from pure films of deutereted hydrocarbons Formation of the D- occurs via dissociative electron attachment and dipolar dissociation processes A single resonant maximum – core excited resonances No desorbing heavier polyatomic ions were observed due to partitioning of the kinetic energy and isotope effects in production of negative ions. ”D- ion desorption from condensed CD4, C2D2, C2D4, C2D6 and C3D8 molecules induced by electron impact” P. Możejko, L. Parenteau, A. D. Bass and L. Sanche, Radiat. Phys. Chem. 68, 215 (2003) © Paweł Możejko ESD from saturated deuterated hydrocarbons ”Intrinsic and extrinsic factors in anion electron-stimulated desorption: D- from deuterated hydrocarbons condensed on Kr and water ice films” P. Możejko, A. D. Bass, L. Parenteau and L. Sanche, J. Chem. Phys. 121, 10181 (2004) © Paweł Możejko ESD from unsaturated deuterated hydrocarbons ”Intrinsic and extrinsic factors in anion electron-stimulated desorption: D- from deuterated hydrocarbons condensed on Kr and water ice films” P. Możejko, A. D. Bass, L. Parenteau and L. Sanche, J. Chem. Phys. 121, 10181 (2004) © Paweł Możejko Results All D- yield functions display a threshold near 7 eV and a single broad resonant maximum The broad resonant like structure is attributed to D- abstraction via DEA e - + CnD2n+2 → CnD2n+2*- → D- + CnD2n+1 e - + CnD2n → CnD2n*- → D- + CnD2n-1 The D- yield functions for submonolayer quantities of the saturated compounds condensed on Kr display a sharp peak in the vicinity of 9.7 eV For unsaturated deuterocarbons the narrow Kr*- feature is absent from the D- yield functions Above 15 eV the ion yield is observed to increase linearly with the incident electron energy indicating the involvement of the direct DD process © Paweł Możejko Perturbation of ESD due to intrinsic and extrinsic effects On nonporous ice – perturbation of the ESD process have only intrinsic character – no extrinsic !!! ִ intrinsic perturbation of DEA due to a transfer of the excess electron from the deuterocarbon anion to either an electron state of (H20)n in the film or an neighboring molecule ִ Intrinsic perturbation of DD for unsaturated molecules due to intrinsic modulation of the autoionization of neutral excited state prior to dissociation On porous ice – porosity of ice introduces extrinsic effect connected with postdissociation interaction – DEA and DD suppressed be a factor of 2 relative to nonporous ice © Paweł Możejko Application in Radiation damage to DNA Radiation affects DNA in two ways: Induces damage that compromises cell function (an origin of cancer) Induces cell death (good in context of radiotherapy) Low-energy secondary electrons are produced in large quantities by ionizing radiation A complete description of the mechanisms responsible for such damage must involved LEE studies on small molecular „sub-units” of DNA, viz., H2O, DNA bases, and sugarphosphate backbone analogues © Paweł Możejko LEE interactions with DNA Very low energy threshold for single and double strand breaks (SSB and DSB) DSB seems to be a single stage (one-electron-hit) process Highly structured dependence on energy Resonances At low electron energies HCNOH-, O- (or NH2-) OCN- and CH- from B. Boudaiffa, P. Cloutier, D. Hunting, Thymine have been M.A. Huels, L.Sanche, observed Science 287 (2000) 1658 Abdoul-Carime et al., Radiat. Res.155 (2001) 625 © Paweł Możejko New things to do Low energy electron (LEE) damage to DNA and its components Reactive scattering within DNA Cross section measurements Cross section calculations © Paweł Możejko Calculations (simple or more sophisticated) P. Możejko and L. Sanche, Radiat. Phys. Chem. 73 (2005) 77-84 P, Możejko and L. Sanche, Radiat. Environ. Biophys. 42 (2003) 201-211 © Paweł Możejko New experiments Low energy electron (LEE) damage to tetrahydrofuran in the presence of N2O LEE damage induced in films of the deoxyribose analogues like 3-hydroxytetrahydrofuran and α-tetrahydrofurfuryl alcohol in the presence of O2 Real living cell contains large amount of water !!! Measurements of LEE induced damage to the deoxyribose analogues (tetrahydrofuran etc) coadsorbed with water and molecular oxygen © Paweł Możejko ESD from condensed multilayers films of deoxyribose analogues Only H- observed to desorb Below 15 eV H- produced by DEA Yields similar for I, II and III so H- probably from furan ring. D. Antic, L. Parenteau, M. Lepage and L. Sanche, J. Phys. Chem. B 103 (1999) 6611 D. Antic, L. Parenteau and L. Sanche, J. Phys. Chem. B 104 (2000) 4711 © Paweł Możejko Reactive Scattering of 1-5 eV O- in Films of Tetrahydrofuran e- + O2(3Σg-) → O2* -(2Πu , 2Σu+, 2Σg +) → O-(2P) + O(3P or 1D) e-(E) + O2 → O2* + e-(E’<E) → O- + O+ + e-(E’<E) O- + C4H8O → [OC4H8O]*- → OH- + C4H7O M. A. Huels, L. Parenteau and L. Sanche, J. Phys. Chem. B 108 (2004) 16303 © Paweł Możejko LEE induced damage in the THF + N2O films O- is produced via dissociative electron attachment (DEA) to condensed N2O molecules: e- + N2O → (N2O)- →N2 + O. In the pure THF film case, His created via DEA to THF: e- + C4H8O → (C4H8O)- → H- + other fragments. We have did not observe Oanions desorbed from the pure film of THF. OH- anionic fragment is produced through reactions of O- with THF molecule e.g. O-+C4H8O→ →OH- + C4H7O (or other fragments). P. Możejko, L. Parenteau A.D. Bass and L. Sanche (2005), to be published © Paweł Możejko 3-hydroxytetrahydrofuran (C4H8O2) and α-tetrahydrofurfuryl alcohol (C5H10O2) condensed onto O2 films The resonant structures in O- desorption signal from multilayer of O2 in vicinity of 5-15 eV are due to DEA to O2 molecules e-+O2 → O2-(2Πu,2Σ+g,u) → O-(2P)+O(3P,1D). None OH- are desorbed from pure films of 3-hydroxytetrahydrofuran and α-tetrahydrofurfuryl alcohol OH- is created in the reactions involving O- and C4H8O2 and C5H10O2 interactions, respectively: O-+C4H8O2 → OH- + other fragments, O-+C5H10O2 → OH- + other fragments. P. Możejko, L. Parenteau, A.D. Bass and L. Sanche (2005), to be published © Paweł Możejko Acknowledgements Paweł Możejko kindly acknowledges financial support from CIHR in the form of a Post-doctoral Fellowship. Contributing Scientists: Léon Sanche Andrew D. Bass Luc Parenteau © Paweł Możejko After hours ... Photo by Bożena Żywicka-Możejko